Immersion heaters



Nov. 4, 1969 M. J. RAPs|s 3,476,915

` IMMERsIoN HEATERS Filed March 17, 1966 FIG 2 /Nl/ENTOR l.| By M/CHAE'L J. @APS/S ATTORNEY United States Patent U.S. Cl. 21,9-523 8 Claims ABSTRACT OF THEv DISCLOSURE An elastomer one-piece head-seal yfor a high resistance immersion heater. This `takes the form of an elbow, one end of which is hollowed out to form a cap which ts over the open end of the frangible heater tube which comprises fused quartz or thelike. The cap makes gripping contact with the tube by means of one or more internal annular ridges. A plug formed integrally with the interior of the cap is forced ush against the end of the tube, closing it except for a small 'channel just suiicient to accommodate the power leads tothe heater. T he channel executes av 90 degree turn and terminates in a-,nipple which protrudes from the upper end of the head-seal, and lits tightly around the outside of the external power conduit. The internal junction between the cap and the frangible tubes, and the external junction between the nipple and the conduit are both completely sealed by a thin coating of adhesive dissolved in a volatile coating for application and comprising the same elastomer base as the body of the head-seal.

T This relates in general to electrical heaters for immrsion in liquid baths and, more particularly, to immersion heaters having fused quartz sheathes, and techniques and structures for sealing the same to connecting conduits.

In accordance with prior art practice, immersion heaters are commonly of a type comprising a coil of wire of high electrical resistance wrapped on a core or mandrel ofceramic, or the like, which is a good radiator. For use in corrosive or high temperature baths, a fused quartz `tube replaces glass or metal sheathing in such a heater. The open end of the quartz sheath or tube is connectedvthrough a head-seal to a cable or conduit for carrying electrical wires to a source of power. In general, theheating'unit is suspended vertically into the bath from an support on the edge of the tank, so that the headseal is maintained above-the level of the liquid; or, alternatively, it is inserted laterally into the bath through a screw-threaded opening in the side of the tank, which isvtted with a screw-in liquid-tight seal, so that the headseal is disposed outside of the tank.

Such arrangements are necessary in accordance with prior art practice because of the diicultyin providing an effective resilient liquid-tight seal to quartz over a satis-factory range of heater operating temperatures, since seals `to quartz which stand up well at room temperature have atendency to deteriorate or breakunder the action of corrosive liquid baths, and/or temperatures of the order of 350 degrees Fahrenheit or more. Moreover, it has been found that structures in which the head-seal is maintained outside of the bath, -and therefore require theunscrewing of a connectingmember from the quartzclad heater for replacement of parts, are hazardous because of the frangibility of the fused-quartz tube. In addition, models which are screwed into a lateral wall of the tankrequireL draining of the heating element. A f t A ygeneral object of the present invention is the improvement of head-seals for immersion heaters with frangible sheaths. More particular objects of the invention are to provide head-seals which are substantially impervious tank in order to remove the Patented Nov. 4, 1969 ice to the corrosive effects of liquids, notwithstanding the high temperatures to which they are heated, retaining a vapor-vent passage to the outer atmosphere through an electrical conduit. Other objects of the invention are to provide a heater particularly `adapted for use in shallow baths; and which is readily removable from the tank for repairs to the heater or the tank.

These and other objects of the invention are achieved in an immersion heater comprising a high resistance heating element enclosed in a frangible sleeve, sealed at one end, encased at the other end in a resilient one-piece head-seal in the form of a cap designed to t over the open end of the frangible tube and constructed to contain a connecting channel adapted to accommodate the electrical leads from the heater and provide a mating junction with a connecting power 'conduit which is substantially impervious to the corrosive elfects of the surrounding high temperature bath.

In a specific embodiment of the invetnion, which is described by way of example, the high resistance heater comprises a coil wound about a ceramic mandrel, the assemblage being encased in a fused-quartz tube which is sealed at one end and open at the other. T wo parallel connecting leads from the heater coil, surrounded by ber glass insulation, pass toward the open end of the quartz tube and are ultimately joined in soldered connections inside of the head-seal with matching leads of the power conduit.

The resilient head-seal is in the form of a hollow cylindrical cap of material which is resistant to heat and corrosion by the active elements in the bath. The inner diameter of the cylinder slightly exceeds the outer diameter of the quartz tube, and the end of which is coated with an adhesive having a base similar to the material of the cylinder. A gripping contact is achieved with the adhesive coated tube end by means of one or more annular ridges on the inner surface of the cylinder.

One end of the cylindrical cap is closed by means of an integrally-formed internal plug which is forced ush against the end of the quartz tube, closing it except for a small channel just suilicient to accommodate the connecting power conduit. The channel executes a ninetydegree turn and terminates at its outer end in a nipple protruding from the curved surface near the end of the cylindrical cap. This nipple is dimensioned to t tightly over the head of the connecting power conduit which extends a substantial depth into the channel. The external junction between thenipple and the conduit is completely sealed by means ofa thin coating of selfcuring adhesive having as its base material similar to that of the cylinder.

` A particular advantage of the heater assemblage of the present invention is that it is resistant to deteriorating action by corrosive, high temperature baths. Other advantages are that it is adapted for total immersion in shallow as well as deep baths and can be readily removed for repairs to the heater or tank without hazard of breakage due to the frangible nature of the sheath.

These and other objects, features, and advantages of the invention will be apparentA tothose skilled in the art upon a detailed study of the specification and claims hereinafter with reference to the attached drawings, in which:

FIGURE 1 is an overall showing of an immersion heater including a head-seal in accordance with the present invention which is disposed horizontally in a supportingcradle in the bath to be heated;

FIGURE 2 is a longitudinal showing of the heater assemblage of the present invention with the right-hand end broken away to disclose the details of the portion including the head-seal; andV FIGURE 3 is a cross-sectional showing of the structure 3 of FIGURE 2 through a plane indicated by the Referring to FIGURE 1 0f the drawings which shows the entire heater assemblage-installed for use, the tank 1,.which is a conventional type of rectangular tankseveral feet wide and several feet deep, is partly lled to a depth of, say, six inches, with a bath 2 which may comprise any liquid. For the purposes of the present illustration, the bath 2 may be assumed to contain an acid or any other liquid which might ordinarily have a corrosive eiect on the elements of the heater assemblage 3.

The overall heater assemblage 3 comprises a heating unit clad in a quartz tube 4, sealed at one end, and encased at the other end in a resilient head-seal 5 in the form of a cylindrical cap which has a nipple protrusion l6 from the top, near the closed end, into which is sealed a resilient conduit 7 leading to a power-connecting plug.v

The assemblage 3, which in the present embodiment has an overall length of about twenty-tive inches and isv a little over an inch in diameter, is mounted in a gridlike cradle 9 of the rectangular cross-section two and onequarter inches on a side, having a length just greater than that of the heater assemblage 3 .The vfused-quartz tube 4 is supported in the cradle 9 by a pair of metal rings 10 and 11 attached to the top of the cradle, which rests in a horizontal position along the bottom of the tank 1. The head-seal 5 ts into the right-hand end of the cradle withnipple -6 protruding through the grill-work. In preferred form, the cradle 9 is formed by a criss-cross grillwork of metal coated with a synthetic resilient material, such as, for example, polyvinyl chloride. The principal function of cradle 9 is to protect the fused-quartz hea'tersheath from breakage, while interfering as little as possible with the radiation of heat into the bath from the heating unit.

Let us refer, now, to the more detailed sectional showings of FIGURES 2 and 3 of the heater assemblage 3, which includes the novel head-seal 5. In the present example, the heating element 12, which is visible in the broken away section of the fused-quartz sheath 4, is constructed to heat up to a maximum temperature of, say, 1500 degrees Fahrenheit. In the present embodiment, this heater comprises a coil of 20 guage Nichrome wire, or the like, wound into a coil 13 which is designed to absorb about 1,000 watts from a 115 volt alternating current source. This is then wound into the spiral notches on a ceramic core or mandrel 14. For example, this may be eighteen inches long, and in the form of a doublepitch screw, having an outer diameter of, say, elevensixteenths of an inch, and a diameter of sevensixteenths of an inch at the root of the threads. There are approximately three screw threads Vto an inch, the Width of the, flat truncated outer portion being approximately oneeighth of an inch. Core 14 may be formed of any ceramic material designed to withstand temperatures in excess of about 1500 degrees Fahrenheit, without melting, cracking, or sustaining any irreversible change, and which `is also a good radiator characterized by a relatively low coefficient of expansion with heating. A preferred mate rial for this purpose is known as cordierite, having a composition 2Mg.O-2Al2O3-5Si02, which is sold by the American Lava Company of Chattanooga, Tenn. under the trade name AlSiMag 202.

Coil 13 is wound about the core or mandrel 14 in such a fashion that both ends 15 and 16 are available at the right-hand end of the heater (referring to the drawing) for respectively fastening them in a pair of wrappedwire connections, only the upper one of which, 17 ,y is shown. Each of these twoy wrapped wire connections mates with a respective one of the low resistance con-A necting terminals 19 and 20, which may, for example, be of nickel-clad copper. These wrapped, soldered connections, including 17, are encased in insulating fiber glass sleeves 21 and 22, the former being shown in section for the purposes of illustration. Wrapped connection17 y and its companion (not shown) their'respectiveisleeves, are further heat-.insulated by means of--ber glasspaeking truding about'one-quarter of an inch from 23, which serves to absorbvya substantial portion of the heat generated in the heating element 12, ahead of headseal 5.

Preferred materials for cap-like head-seals 5 are elastomers, such as silicone rubber, neoprene, or alternatively, a iiuoroelastomer manufactured by E. I. du Pont de Nemours and Company of Wilmington, Del. under the trade name Viton All these materials retain useful characteristics for the purposes of the pr es ent 1inven tion from room temperature to well above 200 degrees Fahrenheit, and in some cases,n`erly 500 degrees Fahrenheit. Over the temperature rangeof interest, the preferred materials exhibit coetcients of thermal expansion cubical) of the order of about between 25 and 50x10-5 inches per inch per degree Fahrenheit, high resilience at all temperatures within the range, and good to excellent swell resistance to liquid absorption. Moreover, they adhere well to the sheath or tube enclosing `the heater, which in the case disclosed is fused quartz, and are so characterized that they do. not crack and pull'away'frorn the junctions uponheating. In addition, they` are good insulators of heat and electricity, resistant to aging ,causedf by heat, light, and oxidation, and highly resista'nt'to reaction with corrosive-acids, chemical solvents, certain types of oils, or whatever components may conceivablyfbe present in the bath in which the heating unit is particularly designed for immersion. Furthermore, the base material should be soluble in a volatile solvent in order to form a sealant to be applied in a manner to be described hereinafter in forming a liquid-tight junction be-i twen the head-seal 5 and the heater assemblage including the open end of the quartz sheath 4. It is contemplated that any elastomer exhibiting these desired characteristics would be useful for the purposes of the present invention.

Resilient head-seal 5 'is'in the form of 'a cylindrical ca'p about two and one-half vinches long and one'and one-half inches in diameter. It is open at one end, forming an inner chamber 24 aboutone and one-half inches along the axis, which is designed to it over the end of the quartz tube 4. In order to improve the grip of headseal 5 on the `quartz tube 4, the chamber 24 includes a plurality of annular ridges 27, which protrude inwardlyl about one-sixteenth of an inch from the inner wall of chamber 24, the wall being aboutone-sixte'en'th ofan inch" thick. Ridges 27 are Vsernicircular in cross-section, about one-sixteenth of an inch in diameter, and are spaced apart about one-'quarter ofan inch. In the present em-f` bodiment, there are four parallel ridges, the rst'of whih, I is at thefedge of chamber 24, the others formingparallel rings spaced apartinside of the chamber.

An internal plug or barrier 25, which is integrally formed into the right-hand end of the cap-like head-seal 5, serves to close ol the chamber 24 except for a central channel 26 about one-half linch in diameterjwhich eXecutes a ninety-degree turn and emerges from the top of the cylinder at the center of the nipple 6, the latterprothe closed end of the cylinder 5.

VIn fabricating the heater assemblage, including head-' seal 5, a'conduit 7, having an outer diameter'A just slightly les than that of channel 26, is forced into place through the nipple `6 to a depth-of'about one inch. Conduit 7vhas a coating 7a about one-sixteenth of an inch thick and'V preferably of the same 'material as the cylindrical elementv 5. The lead wires 29 and 30, encased in conduit"7, may,` for example, be 14 guage stranded copper wire, nickel plated, and having an asbestos and ber glass insulating covering. These leads are stripped at their ends and pulled beyond thee'nd of'conduit 7 and through the end ofA cham- A ber 24 and into the end of tube 4 where they are respectively clamped by the upper connecting Velement 31 and its companion (not shown). The latter, which are'of' any conventional form known'in the art, such'as solder'- the top,y vnear less connectors, are fastened to the respective nickel-clad copper terminals 19 and 20 at positions about one-quarter of an inch inside of the open end of the fused-quartz tube 4. Junction 31 and its companion are then wrapped with an insulated tape to form an insulated junction in the manner shown in 34. The junction 31 and its companion are further insulated by the -fiber glass stuffing in the end of tube 4.

After the internal connections have been completed, that portion of the fused-quartz tube which is designed to come in contact with the annular ridges 27 is first coated with an adhesive sealant 28 having an elastomer base. If the body 5 is formed of neoprene rubber, the sealant 28 is of a type which has a neoprene base dissolved in a highly volatile solvent, so that the coating is self-drying within about one-half hour after application to form an additional thin coating of neoprene. In an alternative embodiment in which, for example, the body 5 is formed of silicone rubber, an alternative adhesive sealant is employed, which has a silicone base, such as, for example, that manufactured by General Electric Company, Inc. under the trade name RTV-106 Red. The portion to be coated is first cleaned to remove dirt and grease, and the sealant is applied just prior to forcing the end of fused-quartz tube 4 into position in the chamber 24, inside of the cap-like head-seal 5, llush against the internal plug 25, in which position the sealant is permitted to dry.

After the internal lead wires are pulled up taut at their ends to make proper connection to plug 8 leading to the power source, one or more coatings of sealant 35 is also applied to the outer surface of the nipple 6 to completely cover and seal-olf the junction to the outer surface of conduit 7. Sealant 35 is substantially the same material as sealant 28, as described in the preceding paragraph.

It will be understood by those skilled in the art that immersion heaters in accordance with the present invention are not restricted to the specic forms, dimensions, or materials disclosed herein by way of example; but, that the scope of the present invention is limited only by the scope of the appended claims.

What lI claim is:

1. In a heater designed for immersion in a liquid bath comprising in combination a high resistance electrical heating element enclosed in a frangible tube having one end sealed and the other end open, wherein the electric terminals of said heating element are drawn out through the open end of said tube and electrically connected to a pair of insulated electrical conductors enclosed in a conduit leading to a source of power, the improvment which comprises:

a fluid-tight head-seal designed for immersion in said bath, said head-seal comprising in combination a hollow cylindrical cap of resilient electrical insulating material which is substantially impervious to the liquid in said bath, said cylindrical cap having an opening at one end of suicient diameter to accommodate the open end of said frangible tube, said opening formed to include a plurality of internal annular ridges dimensioned to grip said tube snugly, said cylindrical cap partially closed at the other end. by an integrally-formed plug designed internally for juxtaposition against the end of said frangible tube, said plug including a passage with an internal diameter just exceeding the external diameter of said conduit and terminating at its external end in connecting means constructed integrally with said cylindrical cap for bringing said conduit into juxtaposition with said passage, and sealing means adapted for application in liquid form which cures to a resilient coating for application at the junction where said frangible tube is joined to said cylindrical cap and to the junction where said connecting means is joined to said conduit, said sealing means comprising y an elastomer base of substantially the same composivtion as said cylindrical cap, dissolved in a highly volatile solvent.

2. The combination in accordance with claim 1 wherein said resilient cylindrical cap comprises an elastomer characterized by high resilience, a cubical coefficient of thermal expansion lying within the range 25 to 50x10*5 inches per inch per degree Fahrenheit, and substantial resistance to the absorption of liquid within a range from room temperature to a temperature well above 200 degrees Fahrenheit.

3. The combination in accordance with claim 2 wherein said resilient cylindrical cap comprises an elastomer adapted to sustain a temperature of at least 200 degrees Fahrenheit without substantial deterioration because of aging, oxidation, heating, and reactions to chemicals including corrosive acids.

4. The combination in accordance with claim 3 wherein said frangible tube comprises fused quartz and said resilient material comprises silicone rubber.

5. The combination in accordance with claim 3 wherein said frangible tube comprises fused quartz and said resilient material -comprises neoprene.

6. The combination in accordance with claim 1 wherein the junction between the open end of said frangible tube and the opening of said resilient cylindrical cap including said annular ridges is formed by applying said sealant in liquid form to the end of said tube prior to fitting said cylindrical element thereon, and wherein said sealant is cured thereafter.

7. The combination in accordance with claim 6 wherein said frangible tube comprises fused quartz, said resilient material comprises silicone rubber and said sealing means comprises a silicone rubber base.

8. The combination in accordance with claim 6 wherein said frangible tube comprises fused quartz, said resilient material comprises neoprene, and said sealing means comprises a neoprene base.

References Cited UNITED STATES PATENTS 1,334,035 3/ 1920 Johnson 219-523 X 2,690,541 9/ 1954 Elliott 174-77 2,904,769 9/ 1959 Sampson et al 174-77 2,977,456 3/1961 Stiebel 219-337 X 3,134,888 5/1964 Ammerman 219--523 3,230,492 1/ 1966 Drugmand et al. 338-274 FOREIGN PATENTS 554,606 3/ 1958 Canada.

647,178 12/ 1950 Great Britain.

969,381 9/ 1964 Great Britain.

ANTHONY BARTIS, Primary Examiner U.S'. C1. X.R. 

